When Human Does Life Begin

The human part of the brain, the cortex, is not fully developed, as shown by "brain waves" on an EEG, until very late in gestation. The "individuating" function of a person's brain doesn't start to come into existence until the outer surface of the cortex begins to develop those deep furrows, grooves, and convolutions (sulci and gyri) that make a human brain look like a walnut, unlike the smooth brains of other animals. The furrows and grooves are what enable our brains to have millions more cells and connections between them than other animals, and so create our humanity. And the precise configuration of the grooves and convolutions are part of what determines our individuality; why, for instance, identical twins have different personalities. However, these structures don't begin to form until the last 2 months of pregnancy.

A "human life" or "human personhood" begins when brain waves are measured on an EEG. That is well into the second half of pregnancy; however, no matter how many times the "40 days" factoid is repeated. (A factoid is the name for a statement repeated often enough that people accept it as truth, though it's not.)
http://eileen.250x.com/Main/Einstein/Brain_Waves.htm
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